Disclosed herein are methods for preparing triglyceride oils containing at least 2% branching on the hydrocarbon chain, said method involving subjecting in a pressurized container (a) a feedstock containing unsaturated fatty acids attached to a glycerol backbone having 6 to 25 carbon atoms or mixtures thereof, (b) modified zeolite, and (c) water or alcohol in the presence of an inert atmosphere (e.g., at a temperature of about 150° C. to about 350° C. and a pressure of about 10 to about 300 psi for about 24 to about 72 hours) to produce triglycerides containing at least 2% branching (and optionally isolating the triglycerides containing at least 2% branching and optionally purifying the isolated triglycerides containing at least 2% branching); wherein the modified zeolite has been calcined at about 760° C. to about 840° C. for about 20 to about 28 hours, then placed in about 1N HCl at about 50° C. to about 60° C. for about 20 to about 28 hours and washed with water until the pH is neutral.
Petroleum-based materials, while generally cheaper to produce than bio-based products, tend to resist the typical degradation found in nature resulting in problems in their waste management (Thomas, C. E. S., Lecture Notes in Energy, 35: 1-8 (2017)). For this reason, strict environmental regulations were imposed upon the use of petroleum-based materials. Particularly, in the lubrication field, there have been tremendous health concerns from the use of synthetic lubricants (Adhvaryu, A., et al., Ind. Crops Prod., 21: 113-119 (2005); Nagendramma, P., and S. Kaul, Renew. Sustain. Energy Rev., 16: 764-774 (2012)). These products have been shown to be harmful to the environment and have been found in the water, soil and air (Adhvaryu, A., et al., 2012; Nagendramma, P., and S. Kaul, 2012). Therefore, further development of novel technologies to convert bio-based oils into value-added bio-based products would reduce global tension over petroleum resources and mitigate climate change (Biermann, U., et al., Angew. Chem. Int. Ed., 39: 2206-2224 (2000)).
Vegetable oils (i.e., triglycerides) are currently used in the industry as bio-lubricants. Unfortunately, these oils are not stable at high temperatures and are viscous at low temperatures (Battersby, N. S., et al., Chemosphere, 24: 1998-2000 (1992); Becker, R., and A. Knorr, Lubr. Sci., 8: 95-117 (1996)). These drawbacks have prevented them from being widely adopted. Modification of triglycerides is the most direct way to overcome these two drawbacks. Particularly, branching on the carbon chains of the triglycerides can potentially reduce their freezing points because of the disruption of the molecular packing of the oils. This reduces the probability of crystal formation in cold climates. For example, the melting point of the methyl ester of palmitic acid, a linear 16 carbon saturated fatty acid, is 30° C. (Knothe, G., and R. O. Dunn, JOACS, 86:843-856 (2009)). On the other hand, the 16 carbon fatty acid 15 carbons long chain with a methyl branch at carbon 14 has a melting point of 16.8° C. (Knothe, G., and R. O. Dunn, 2009). The melting point falls progressively as the position of the methyl recedes from the ends of the molecule. The ester branched-chain canola oils prepared from a two-step heterogeneous process (epoxidation followed by ring opening) also showed a significantly lower pour-point property after modification (Madankar, C. S., et al., Ind. Crops and Prod., 44: 139-144 (2013)). These modified canola oils maintained a stable lubricating film to prevent the wear of metal surfaces (Madankar, C. S., et al., 2013). Palm oils with high saturation level (50% fatty acids (FA)) are not widely used as lubricants. Pillai et al. (Pillai, P. K. S, et al., Ind. Crops Prod., 84: 205-223 (2016)) expanded the use of these oils by using a cross metathesis method followed by epoxidation and hydroxylation to produce functionalized polyol palm oils. These polyol products were found to have low-melting point properties (Pillai, P. K. S, et al., 2016)). Isomerization of oils (in the form of FA) to introduce methyl-branching on the alkyl FA was explored by several research groups to improve the low temperature property of the materials (U.S. Pat. No. 6,946,567; U.S. Pat. No. 5,677,473; EP 0774451A1). Particularly, the work on the zeolite-Lewis base combination isomerization process was found to be the most efficient system to produce methyl-branched-chain FA (MBC-FA) to date (Ngo, H. L., et al., Eur. J. Lipid Sci. Technol., 114: 213-221 (2012); U.S. Pat. No. 9,115,076). The products were reported to have excellent low temperature properties and good lubricity properties (Ngo, H. L., et al., Eur. J. Lipid Sci. Technol., 113: 180-188 (2011); Ngo, H., et al., Eur. J. Lipid Sci. Technol., 118: 1915-1925 (2016)). In addition, this isomerization process generated low by-product levels and have these attractive advantages over prior systems, including (1) ready recovery by filtration, (2) reuse 20 recycles having been achieved without significant loss of activity or selectivity, and (3) an absence of added organic solvent (Ngo, H. L., Eur. J. Lipid Sci. Technol., 116: 645-652 (2014)).
To increase the functional fluid consumption of branching bio-based products, we developed a new fatty acid isomerization system. We have developed methods to convert of triglycerides (e.g., natural plant oils) containing unsaturated hydrocarbon chains using a modified zeolite as a heterogeneous catalyst into triglycerides generally containing at least about 2% branching and up to about 30% branching (methyl-branched-chain triglycerides (MBC-TG)) which can be used, for example, for lubrication purposes. The isomerization generally involved the presence of a modified zeolite (e.g., H+-BETA) catalyst and water (or alcohol) co-catalyst at various reaction temperatures and reaction times.